Method of manufacturing a combustion enclosure with cooling by transpiration

ABSTRACT

The invention relates to a method of manufacturing an enclosure containing hot gases cooled by transpiration. The enclosure comprises a porous wall and means for applying a cooling fluid to the outside face of the porous wall to cause a flow of cooling fluid to pass through the porous wall by transpiration. The cooling fluid application means is formed by disposing a plurality of cooling liquid distribution pipes regularly around the porous wall and terminating tangentially on its outside face in a plurality of superposed horizontal injection levels. Feed channels are provided crossing substantially perpendicularly through the distribution pipes, formed between each of them, and connected to cooling liquid feed means. Calibration ducts of determined section are provided, connecting, at each of the injection levels, the vertical feed channels to the horizontal distribution pipes surrounding them, to deliver predetermined headloss to the inside face of the porous wall. The headloss is adapted as a function of the zone to be cooled to optimize cooling flow rates along the porous wall.

This application is a division of U.S. Ser. No. 08/637,441, filed Apr.25, 1996, now U.S. Pat. No. 5,732,883.

FIELD OF THE INVENTION

The present invention relates to using transpiration to cool anenclosure containing hot gases such as a hot gas line, a boiler, or acombustion chamber of a rocket engine, or of a gas generator, or of aprechamber.

PRIOR ART

Various systems are already known for cooling porous walls bytranspiration.

The flux, known as "transpiration", of a cold fluid from a first face ofa porous wall situated on the same side as a low temperature sourcetowards the second face of the porous wall situated on the same side asa high temperature source takes place with heat transfer occurringwithin the porous wall. The porous wall is the seat of two heat fluxesin opposite directions, namely a conduction flux conveyed by the solidmatrix and an advection flux conveyed by the fluid. These two fluxesinteract while exchanging power in application of an exchange mechanismknown as "transvection" which, at the microscopic level of the pores,corresponds to peripheral convection of the fluid in contact with thesolid matrix. This transfer of heat from the hotter wall towards thecooler fluid modifies the two opposing fluxes of conduction and ofadvection. The power extracted from the incident conduction flux istaken up by the advection flux conveyed by the fluid and is returned toits origin, i.e. to the high temperature source. The conduction fluxprogressing towards the cold zone is thus reduced by this extractedpower. The intensity of the thermal coupling within the wall between thewall material and the fluid, i.e. the internal heat exchangecoefficient, depends on the internal geometry of the porous medium, onthe nature of the fluid, and on the flow rate of the flow.

Cooling by transpiration has already been considered for a rocket enginepropulsion chamber whose wall is exposed on one of its faces to the heatflux coming from the combustion and which must nevertheless bemaintained at a temperature below the acceptable limit for the materialfrom which it is made and compatible with mechanical strengthrequirements. In such cooling by transpiration, the low temperaturesource is constituted by one of the propellant components that is atambient or cryogenic temperature, and the wall of the chamber is made ofa porous material that is permeable to the cooling propellant component.The transpiration flow passes through the wall prior to being dischargedinto the combustion chamber. On its path, the fluid takes up heat powerfrom the wall, and as a result keeps it within an acceptable temperaturelimit. A second cooling effect is also obtained because the fluiddischarged into the chamber interposes itself between the wall and thecombustion, thereby creating an obstacle to the incident heat flux, evenbefore it reaches the wall.

U.S. Pat. No. 3,832,290 and U.S. Pat. No. 3,910,039 thus describe arocket engine combustion chamber having a porous wall with ribs appliedto the external face thereof to constitute approximately rectangularfluid application compartments that are regularly distributed over theentire periphery of the chamber. An outer intermediate wall defines theoutside face of the compartments remote from the porous wall. A singlecalibrated cooling fluid feed orifice is formed in each compartmentthrough the outer intermediate wall to adjust the value of thelooked-for transpiration flow rate in each compartment. The devicesdescribed thus make it possible to achieve a degree of adjustment of thetranspiration cooling flow rate so as to match the various zones of thechamber to constant porosity for the inside wall, but such matching canbe performed only in discontinuous manner from one compartment toanother. In addition, making known combustion chambers capable ofenabling cooling to be performed by transpiration requires a largeamount of machining and thus gives rise to a high manufacturing cost.

In application FR 2 691 209, previously filed by the Applicant, thecooling fluid flow rate is controlled progressively and continuouslyover the entire section of the enclosure, firstly by using a sheathwhich, by being applied directly against the outside face of the porouswall provides spatially-modulated hydraulic calibration, and secondly byproviding a local perforation density that can vary progressively,defining within each section a cooling fluid rate through the porouswall which matches the heat flux applied to the inside face of theporous wall. However, the techniques used for making such an enclosurerequire advanced technologies. In addition, the mechanical strength ofthe enclosure obtained in that way is very closely tied to thedimensioning and the choice of material for the sheath, and also to thecooling fluid flow conditions.

OBJECT AND BRIEF DESCRIPTION OF THE INVENTION

The invention seeks to mitigate the above-specified drawbacks byenlarging the field of application of present cooling systems resultingfrom transpiration from the porous wall of an enclosure containing hotgases, and to simplify the making of such an enclosure.

These objects are achieved by an enclosure containing hot gases cooledby transpiration and a method of manufacturing the enclosure. Theenclosure comprises a porous wall whose inside face forms the internalwall of the enclosure, and means for applying a cooling fluid to theoutside face of the porous wall, which means are located between theinternal wall of the enclosure and an external sealing body of theenclosure, to cause a flow of cooling fluid to pass by transpirationthrough the porous wall,

wherein the means for applying cooling fluid comprise a plurality ofcooling liquid distribution pipes regularly disposed around the porouswall and terminating tangentially on the outside face thereof in aplurality of superposed horizontal injection levels, and feed channelscrossing substantially perpendicularly through the distribution pipesextending between each of them and connected to cooling liquid feedmeans, calibration ducts of determined section connecting, at eachinjection level, each of the vertical feed channels to two horizontaldistribution pipes surrounding them so as to provide predeterminedheadloss at the inside face of the porous wall, which headloss isadjusted as a function of the zone to be cooled so as to optimize thecooling flow rates along the porous wall.

The porous wall may form only a central portion of the inner wall of theenclosure, the non-central portions of the inner wall of the enclosurebeing constituted by inner envelopes mounted to extend the porous walland advantageously being fixed by being welded to opposite ends thereof.

With this particular structure, it is possible to obtain much greaterpairs of enclosure diameter and of enclosure pressure than thosepresently in existence, and to obtain much better control of enclosurecooling. In addition, since the calibration ducts are situated upstreamfrom the porous wall, they are protected from the hot gases, therebyavoiding any risk of failure by an avalanche effect.

Preferably, each envelope is held at its end that is not in contact withthe porous wall by flexible spring-effect metal elements connected tothe enclosure body, and each inner envelope includes a plurality ofmutually adjacent circulation channels closed by a shell assembled onthe outside surface of the envelope, and defining a cavity in which thecooling liquid flows.

The cooling fluid comes from a feed torus disposed at one end of theenclosure and opening to the cavity.

Each feed channel of the central portion of the enclosure opens out atits two ends into respective upstream and downstream annulardistribution grooves into which the circulation channels also open out.

In a first embodiment tending to limit cooling liquid leakage, the endof each distribution pipe remote from the porous wall is closed by aplug. In a second embodiment, all the distribution pipe ends remote fromthe porous wall are closed simultaneously by one or more circularlysymmetrical plates.

Preferably, the distribution pipes are of polygonal or circular section.

In a first embodiment of the porous wall, it is constituted bysuperposed layers of metal cloth having determined pore size, highmechanical strength, and deposited on the inside surface of theenclosure by hot rolling. In a second embodiment, the porous wall ismade directly on the inside surface of the enclosure by plasma formingor by a powder metallurgy technique using a one- or two-componentpowder. In a third embodiment, the porous wall is constituted by aconductive metal sheet having a plurality of microholes, the wall beinghot- formed on the inside surface of the enclosure and being weldedthereto by diffusion.

Advantageously, the cooling fluid is a cryogenic fluid.

The enclosure may be constituted by a propulsion chamber of a rocketengine whose throat ring forms the central portion of the enclosure.

The present invention also provides a method of manufacturing anenclosure containing hot gases cooled by transpiration, in which aninternal portion of the enclosure is made initially, after which aporous wall is formed on the inside face of said internal portion, andthen the assembly is engaged in an outer body of the enclosure, wherein,to make the internal portion of the enclosure which is constituted by astructural part, distribution pipes are pierced for conveying thecooling liquid to the porous wall, feed channels are pierced for feedingsaid distribution pipes with cooling liquid, and calibration ducts arepierced connecting said feed channels to said distribution pipes, and ofa section that defines determined headloss, after which each of thedistribution pipes is closed by an insert fitting exactly to the insidedimensions of the distribution pipe in which it is inserted.

The inserts are made of a material that is incompatible with anyadherence or welding with the material forming the porous wall thatcovers the inside face of the central portion, which makes them easy toremove, mechanically or chemically, after the porous wall has beenformed and without damaging it.

The porous wall may be made by hot rolling superposed layers of metalcloth on the inside surface of the inner portion of the enclosure, thepore size of the cloth being determined and its mechanical strengthbeing high, either directly on the inside surface of the central portionof the enclosure by plasma forming or by a powder metallurgy technique.With such a technique, when using a two-component powder, it ispossible, after compacting, to eliminate one of the two components ofthe powder by chemical means, thereby creating the desired wallporosity. Nevertheless, more conventionally, the porous wall may merelybe made by diffusion welding a hot-formed conductive metal sheetincluding a plurality of microholes to the inside surface of the innerportion of the enclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention appear from thefollowing description of particular embodiments, given with reference tothe accompanying drawings, in which:

FIG. 1 is an axial half-section view of a particular embodiment of adevice of the invention for cooling by transpiration as applied to arocket engine combustion chamber;

FIGS. 2 to 5 are fragmentary sections on planes II, III, IV, and Vrespectively of FIG. 1;

FIG. 6 is a perspective view of the throat ring with inserts forimplementing cooling liquid distribution pipes; and

FIG. 7 is a diagram showing how the various inserts are mutually engagedin the throat ring.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

Reference is initially made to FIGS. 1 to 5 which, by way of example,show an enclosure containing hot gases and constituted by a propulsionchamber of a rocket engine.

A propulsion chamber is conventionally made up of a chamber body 10which serves both to transmit mechanical forces and to provide sealingrelative to the outside, being generally venturi-shaped, having aconverging portion and a diverging portion, an inner envelope 12 whichconstitutes the internal wall of the propulsion chamber, and a cavity 14defined between the chamber body 10 and the inner envelope 12, andenabling a cooling liquid to circulate.

In the embodiment shown, which relates to a conventional regenerativecircuit, the cavity 14 for cooling liquid circulation is made up of aplurality of mutually adjacent circulation channels 15 made in the innerenvelope 12. When these channels are made by milling, a shell 16 isassembled on the outside surface of the envelope by brazing or byelectro-erosion, in order to close the cavity (FIG. 5).

In accordance with the invention, the inner envelope 12 which is incontact with the hot gases is interrupted at least at the throat of thenozzle so as to integrate therein a porous wall 20 which serves firstlya conventional function of confining the flow of combustion gases in thespace defined by said circularly symmetrical wall, and secondly servesto establish heat exchange between the heat flux coming from thecombustion gases and the cooling liquid which is applied to the outsideface of the porous wall 20 to "transpire" through the wall. An innerenvelope formed in this way has two portions which extend the porouswall 20 in opposite directions, and they are held at each end to thechamber body 10 by flexible metal elements 22 providing a spring effectso as to accommodate differential thermal expansion between the porouswall and the envelope.

A ring 18 situated at the throat of the nozzle and made of a materialhaving both good conductivity and good mechanical strength, such as acopper-based alloy, is interposed between the porous wall 20 and thechamber body 10 and includes means for applying the cooling fluid to theoutside face of the porous wall. The throat ring 18 is fixed to thechamber body 10 by fastening means 24, e.g. constituted by hook-shapedprojections present on the body and engaging the ring, or by assemblyzones between the ring and the chamber (e.g. an assembly ring).

The choice of a composite structure comprising both a metal (on thesubstantially cylindrical portion towards the injector and on theconical portion in the diverging portion of the chamber), and a porousmaterial (at the throat) for making the propulsion chamber is justifiedby the fact that it is in the vicinity of the nozzle throat that theincident heat flux is locally greatest, and consequently it isspecifically at that location where cooling must be the most effective(without excessive headloss). Nevertheless, it is possible to envisage astructure without metal portions in which the porous wall 20 covers theentire enclosure, thereby avoiding any need to use an inner envelope 12for ensuring continuity of the inside wall of the enclosure, as before.

The porous wall 20 has a permeable structure, and its thickness may be afew millimeters, having a grain size lying in the range 50 μm to 200 μmand including a sufficient number of open pores to avoid calibrating theflow in this zone. As explained more fully below, the wall may be madeof superposed layers of metal cloth, or more conventionally, by a metalmaterial manufactured by powder metallurgy, or by a conductive metalsheet provided with microholes.

In accordance with the invention, the cooling fluid is bought to theporous wall 20 by a plurality of distribution pipes 30 formed in thethroat ring 18 and regularly distributed around the chamber. These pipes30, all of which terminate tangentially to the porous wall 20, aredisposed in a plurality of superposed injection levels along the entirelength of the throat. They are fed with cooling liquid from feedchannels 32 which cross through the pipes substantially perpendicularlyand which are united at either end of the throat in downstream andupstream distribution grooves 33 disposed at the inlet to the cavity 14and into which the circulation channels 15 open out. A link at eachinjection level between each of the feed channels 32 and the twosurrounding distribution pipes 30 is provided by two calibration ducts34 of section that is determined to obtain the desired headloss and thatis adjusted as a function of the zone to be cooled so as to optimizecooling flows along the porous wall 20. Thus, the cooling fluid passesfrom the upstream circulation channels 15 to the distribution groove 33which then feeds the channels 32 (feed channels of the porous wall)after which the fluid that remains passes into the groove 33 and istaken away by the channels 15 to go to the injector.

In order to enable the cooling flow rates to be maintained practicallyconstant and in order to limit leakage, the various distribution pipes30 are closed at their ends remote from the porous wall 20, eitherindividually by using plugs 36, for example, or else collectively usingone or more superposed circularly symmetrical plates 38 shrink-fitted onthe throat ring (see FIG. 4 where both variants are deliberately shownsimultaneously). Similarly, on the hot gas side, the cooling liquidcoming from the distribution pipes 30 can be distributed via a groove 19situated immediately behind the porous wall 20 and at which the pipes 30terminate.

Within the ring 18, the cooling fluid that is going to transpire passesfrom the channels 32 towards the calibration ducts 34 and then along thepipes 30, and finally towards each groove 19 prior to passing into theporous wall 20.

The cooling fluid is preferably a cryogenic fluid, such as one of thepropellant components of the rocket engine, and it may be delivered tothe various circulation channels 15 from a feed torus 40, e.g. disposedat the junction between the rocket engine nozzle and the divergingelement fitted downstream therefrom (when cooling by means of aregenerative circuit). Nevertheless, the structure of the invention isentirely usable with more conventional cooling by taking a fraction ofthe injection fluid from the injector of the rocket engine ("dump"cooling).

Various methods of manufacturing an enclosure, such as a rocket enginepropulsion chamber, are described below as examples, each implementing asystem of the invention for cooling by transpiration.

Firstly, the chamber body 10 is manufactured as a single piece byforging or casting or by any other conventional technique. The throatring 18 (FIG. 5) is likewise manufactured in conventional manner, e.g.by machining, with the distribution pipes 30 being formed selectively inthe throat in a determined injection configuration (depending on thedesired number of pipes and of injection levels). The pipes arepreferably circular in section, but it is also possible to use anypolygonal section, e.g. square. The feed channels 32 are then piercedbetween each of the various distribution pipes 30 in a planesubstantially perpendicular thereto (e.g. by milling or by EDMmachining). Finally, the calibration ducts 34 are pierced from theoutside surface of the ring 18 to run from one distribution pipe toanother, passing through a feed channel.

Inserts 50 in the form of pins whose outside dimensions match the insidedimensions of the pipes are made of a material which is selected so asto ensure that no adhesion or welding can take place between the pinsand the porous material used subsequently for making the porous wall 20.Each distribution pipe 30 receives a respective insert so as to occupyits volume exactly, and the ends of the inserts are machined so as toguarantee a uniform inside surface for the throat ring (FIG. 6).

Three different techniques can be used for making the porous wall 20. Ina first method, a hot rolling technique is used to deposit on the insidesurface of the throat ring 18 superposed metal cloths of the type knownunder the name Dynapore from Michigan Dynamics (USA) or Rigimesh fromThyssen (Germany). This causes the wires of the cloths to be welded bydiffusion to one another and to the ring 18 with the exception of thespaces corresponding to the ends of the inserts 50 (the inserts being,by design, made of a material that is incompatible with such adherence).In a second method, the porous material is merely deposited on theinside face of the ring 18 which then constitutes a substrate,deposition being by plasma forming or by a powder metallurgy technique.After the material forming the porous wall 20 has been deposited, theinserts 50 are removed mechanically or chemically so as to leave in theinside wall of the ring, an annular manifold 19 at each injection levelwith the section thereof depending on that of the inserts (although alarger section may also be envisaged), with the various distributionpipes 30 terminating therein. It may be observed that the powder isadvantageously a two-component powder, with one of the two components ofthe powder being suitable for being eliminated chemically aftercompacting so as to create determined porosity in the wall 20. Finally,in a third method, the porous wall 20 may merely be constituted by aconductive metal sheet (e.g. of copper) pierced by microholes (e.g. madeby a laser technique) that is hot-formed on the ring 18 and is thendiffusion welded to the inside face of said ring.

The throat ring 18 provided with its porous wall 20 can then be mountedin the chamber body 10, with the fastening means 24 on the bodyguaranteeing proper assembly. Finally, the inside wall of the propulsionchamber is finished off by installing the inner envelopes 12 which arewelded to the ends of the ring 18 via two lips left upstream anddownstream from the ring 18. These lips and the welds can be cooled by avery thin film of fresh propellant taken from the regenerative coolingcircuit. The two portions of the envelope 12 are made conventionally bymilling and then they are closed by means of a shell-forming wall 16either by electrodeposition or by brazing. It is recalled that this laststep of adding inner envelopes 12 is justified only when the porous wallconstitutes a portion only of the inside wall of the enclosure.

It is important to observe that although it is assumed above that thechamber body is previously manufactured by conventional techniques, ittoo could be made by an electrodeposition method once the innerenvelopes 12 have been assembled to the ring 18 and the porous wall 20has been formed on said ring. Naturally, masks would need to be providedto protect the envelopes and the porous wall during such anelectrodeposition step.

The propulsion chamber obtained in this way is particularly suited tohigh combustion pressures (greater than 200 bars for medium- andhigh-thrust engines). In addition, because the chamber body isvoluntarily separate from the cooling system, it is possible to decouplethe function of cooling from the function of providing mechanicalstrength, thereby making it possible to make the chamber body out ofmaterials having very high characteristics for taking up general forcesand pressure forces while the internal cooling system is not greatlyloaded, even at the throat of the nozzle.

In addition, and this constitutes another major advantage of the presentstructure, flow rate calibration is performed by calibration ductsdisposed a considerable distance upstream from the porous wall, therebymaking it possible to maintain an acceptable level of cooling even ifthe porosity of the wall should decrease due to compression under theeffect of the temperature increase of the wall subjected to the hotcombustion gases, thus making it possible to avoid any destructiveeffect.

We claim:
 1. A method of manufacturing an enclosure containing hot gasescooled by transpiration, the method comprising:forming an internalportion of the enclosure comprising:providing a structural part havingan inside face and an outside face, providing distribution pipes in thestructural part located to convey a cooling liquid to the inside face ofthe internal portion, providing feed channels in the structural partlocated to feed the distribution pipes with the cooling liquid,providing calibration ducts in the structural part located to connectthe feed channels to the distribution pipes, the calibration ductshaving a section that defines a determined headloss, and closing thedistribution pipes with inserts, the inserts sized to fit insidedimensions of the distribution pipes in which the inserts are inserted;forming a porous wall on the inside face of the internal portion; andengaging the internal portion and the porous wall in an outer body ofthe enclosure.
 2. The method of claim 1, further comprising forming theinserts of a material that is incompatible with adherence or weldingwith a material forming the porous wall.
 3. The method of claim 1,further comprising removing the inserts after the porous wall has beenformed on the inside face of the internal portion and before theinternal portion and the porous wall have been engaged in the outerbody.
 4. The method of claim 1, further comprising forming the outerbody by electrodeposition of a metal on the outside surface of theinternal portion.
 5. The method of claim 4, wherein the metal comprisesnickel.
 6. The method of claim 1, further comprising forming theinternal portion only in a central portion of the enclosure, two innerenvelope portions being added to the central portion for ensuringcontinuity of the enclosure.
 7. The method of claim 6, furthercomprising forming a rocket engine propulsion chamber with theenclosure, the central portion of the enclosure forming a nozzle throat.8. The method of claim 1, further comprising forming the porous wall byhot rolling superposed layers of metal cloth on the inside face of theinternal portion, the metal cloth having a determined pore size and highmechanical strength.
 9. The method of claim 1, further comprisingforming the porous wall directly on the inside face of the internalportion by plasma forming or by a powder metallurgy technique.
 10. Themethod of claim 8, further comprising forming the porous wall by using atwo-component powder, one of the two components being eliminatedchemically after compacting to create a determined porosity.
 11. Themethod of claim 1, further comprising forming the porous wall bydiffusion welding a hot-formed conductive metal sheet including aplurality of microholes to the inside face of the internal portion. 12.The method of claim 1, further comprising forming a rocket enginepropulsion chamber with the enclosure.